Device for localizing a transmitter unit

ABSTRACT

A device for localizing a transmitter unit. The device includes a base unit and at least one transmitter. The transmitter unit includes an attachment operable to attach the transmitter unit to an object. A transmitter member is arranged to transmit a signal having a determined frequency content. The base unit is arranged to receive the signal from the transmitter member and includes at least two antennas that are positioned a relatively small distance from each other and are arranged to sense the signal. The base unit includes a processing member that is arranged to calculate at least the direction to the transmitter unit utilizing the signal sensed by the antennas. The transmitter unit includes a receiver member. The base unit includes a transmitter member. The transmitter member of the base unit and the receiver member of the transmitter unit are arranged to communicate with a protocol.

THE BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention refers to a device for localising a transmitterunit.

Today many people have difficulties to know where different things orobjects are located, for instance with regard to such things as keys,cellular telephones, bicycles or other vehicles, bags etc. The problemought to be more significant due to the growing amount of things whichwe uses daily. The problem does not only concern things or objects butalso the difficulty to know the position of domestic animals or otherindividuals, for instance children.

U.S. Pat. No. 4,954,836 discloses an arrangement for determining theposition of a transmitter For the determination of the position, severalantennas which are located at different positions are utilized. Theantennas are positioned at a large distance from each other.

U.S. Pat. No. 5,513,854 discloses a system for following the position ofone or several persons moving on a field, in particular a sports field,and which each carries a micro transmitter. The set of antennas isprovided to receive signals from the micro transmitters. The antennasare provided at a large distance from each other.

U.S. Pat. No. 5,021,794 discloses a system for localising personscarrying a micro transmitter. A plurality of mobile receivers isprovided to receive a signal from a micro transmitter and for localisingthe micro transmitter with respect to the direction and the distance.

In these known devices the receiving arrangements have a complicatedstructure comprising several separate units.

WO97/43660 discloses a device for localising and detecting a microwavesource at short distance within an area. The device comprises at leastfour antennas arranged in two pairs. The phase displacement between thesignals to the two antennas in each pair is calculated and by means ofthe calculated phase displacement the source is localised.

SUMMARY OF THE INVENTION

The object of the present invention is to provide improved possibilitiesto supervise different objects and/or persons.

This object is obtained by the device initially defined, which ischaracterised in that the base unit comprises at least two antennas,which are positioned at a relatively small distance from each other andwhich each is arranged to sense said signal, and a processing memberwhich is arranged to calculate at least the direction to saidtransmitter unit by means of the signals sensed by the antennas. By sucha single base unit, the determination of the direction may be made in asimple manner. Since the antennas are provided at a small distance fromeach other, the base unit may have small dimensions and a compact shape.Consequently, the base unit may be carried by one person. Thanks to theattachment means comprised by the transmitter unit, which preferably hassmall dimensions, the transmitter unit may be attached to an arbitraryobject, a person or an animal, the position of which thus may besupervised.

According to an embodiment of the invention, said signal is sensed by aphase displacement between the different antennas due to said distancebetween the antennas. Thereby, the processing member may be arranged tomeasure this phase displacement and to calculate said direction by meansof the phase displacement measured. Thereby, a first and a second ofthree separate antennas may form a first pair of antennas, wherein afirst phase displacement of the signal received between these twoantennas is determined. and the second and the third of the antennasform a second pair of antennas, wherein a second phase displacement ofthe signal received between these two antennas is determined, By meansof the first and the second phase displacement said direction from eachof said pairs may be calculated. It is also possible by means of thefirst and the second phase displacement to determine at least oneapproximate position of said transmitter unit.

According to a further embodiment of the invention, said transmitterunit comprises a receiver member and the base unit a transmitter member.Consequently, it is possible to let the base unit be arranged totransmit a signal to said transmitter unit which may be arranged totransmit the signal back to the base unit, wherein the processing membermay be arranged to measure the time period from the transmission of thesignal to the transmitter unit until the signal is received by the baseunit, and by means of the time period measured to determine the distanceto said transmitter unit. In such a manner, it is also possible, inaddition to the determination of the direction to the transmitter unit,also to obtain a proper knowledge about the distance from the bass unitto the transmitter unit. Advantageously, the processing member may bearranged to Galculate the position of said transmitter unit by means ofthe determined direction, obtainable by means of one single pair ofantennas, and the determined distance, obtainable by means of one or twoof the antennas of said single pair.

According to a further embodiment of the invention, the base unit may bearranged to activate the transmitter member of the transmitter unit by atransmission permission which is transferred to the transmitter unit viathe transmitter member of the base unit and the receiver member of thetransmitter unit. In such a manner. the transmitter member of thetransmitter unit may be activated only when its position Is to bedetermined, which reduces the energy consumption in comparison with ifthe transmitter member of the transmitter unit would have beencontinuously activated.

Advantageously, the transmitter member of the, base unit and thereceiver member of the transmitter unit may be arranged to transfer saidtransmission permission by means of a protocol, preferably a CDMA/CDprotocol.

According to a further embodiment of the Invention, each of saidantennas comprises an essentially straight antenna. Advantageously, theantennas may extend in essentially the same direction. The distancebetween two adjacent antennas may be less than 1 meter, preferably lessthan 60 cm and in particular about 30 cm. The resolution of thedetermination of the position is controlled by the distance between theantennas. Preferably, the antennas may be arranged in a circularconfiguration which results in a satisfactory spatial resolution.

According to a further embodiment of the invention, the base unit ismobile, either as a portable unit or for instance mounted in or to avehicle.

According to a further embodiment of the invention, the device comprisesat least two transmitter units, wherein each transmitter unit isarranged to transmit a signal according to an identification protocoland wherein the base unit is arranged to identify the transmitter unitin question by means of said identification protocol. In such a mannerit is possible for a user to supervise the position of a very largenumber of objects by only one base unit.

According to a further embodiment of the invention, a display member isarranged to display information about said position of said transmitterunit to a user. The display member may be an integrated part of the baseunit or may be formed by a unit, such as a computer or a screen,connected to the base unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now to be explained more closely by a description ofdifferent embodiments and with reference to the drawings attached.

FIG. 1 discloses schematically a device having a base unit and a numberof transmitter units according to an embodiment of the invention.

FIG. 2 discloses schematically the structure of the base unit.

FIG. 3 discloses schematically the structure of a transmitter unit.

DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS OF THE INVENTION

FIG. 1 discloses a device for localising or determining the position ofa transmitter unit 2. The disclosed device or arrangement comprises abase unit 1 and two transmitter units 2. The transmitter units 2comprises means enabling attachment of the transmitter units 2 to anobject 3, which in FIG. 1 is exemplified by a bag. The transmitter unit2 may also be attached to any other things, objects, or animals orchildren. The second transmitter unit 2, which is disclosed in FIG. 1,is provided on a tape-like member 4 enabling attachment to an arbitraryobject. Also other types of attachment members may be utilised, forinstance different types of clamps, safety pins, or the like.Consequently, the transmitter units 2 have small dimensions and acharacteristic essentially flat shape. Each transmitter unit 2 comprisesan antenna 5 schematically disclosed. Although FIG. 1 discloses only twotransmitter units 2, it is to be noted that the device according to theinvention may comprise a very large, essentially arbitrary number oftransmitter units 2.

Each transmitter unit 2 comprises, see FIG. 3, a transmitter member 6which is arranged to transmit a signal having a determined frequencycontent. The base unit 1 comprises at least two antennas 7 and areceiver member 8, see FIG. 2, which is arranged to receive said signalfrom the transmitter units 2. As appears from FIG. 1, the antennas 7 ofthe base unit 1 are positioned in a circular configuration and at arelatively small distance a from each other. The distance a between twoadjacent antennas 7 is less than 1 m, preferably less than 60 cm and maybe for instance 40, 30, 20 or 10 cm. The antennas 7 are designed asessentially straight metal rods which possibly may be extendable andwhich extend in essentially the same direction. Preferably, the antennas7 are demountable in a simple manner by a user. It is to be noted thatit is also possible to design the antennas 7 in other ways and toposition the antennas 7 in any other configuration, for instance atriangular configuration or along a straight line. It is also possibleto arrange the antennas 7 In such a manner that they are directedradially outwardly for instance from a common center point. In FIG. 2,the device includes six antennas 7 and 19 Although the device willfunction with only two antennas 7 for a determination in two dimensionsand with three antennas for a determination in three dimensions, thenumber of antennas may vary. It is considered that the accuracy of thedetermination of the direction to and thus the position the transmitterunit 2 in question may increase with the number of antennas 7. In caseof several antennas 7, the result may be filtered, wherein distortion,noise and/or an incorrect position may be disregarded. In particular, itmay be advantageous to use 6-9 antennas 7, for instance 7 or 8 antennas7. Due to the distance a between the antennas 7 in a three-dimensionalspace, a signal having the determined frequency content from atransmitter unit 2 will hit different antennas 7 at different points oftimes.

Due to this time difference the signal will be sensed by the antennas 7with a phase displacement between the different antennas 7 Such a phasedisplacement is detectable. Thereby, a first and second of the threeseparate antennas 7 may form a first pair, wherein a first phasedisplacement of the signal received between these two antennas 7 isdetermined. and the second and the third of the antennas 7 may form asecond pair, wherein a second phase displacement of the signal receivedbetween these two antennas 7 is determined. By the knowledge about thedistance a between the different antennas 7 and by means of the firstand the second phase displacement, the direction from the base unit 1 tothe transmitter unit 2 may be calculated. It is also possible todetermine, by means of the first and the second phase displacement, atleast an approximate position of the transmitter unit 2 in question andthus of the objects 3 to be supervised

One example of a possible construction of the base unit 1 is disclosedin FIG. 2 The base unit 1 disclosed comprises a processing member 9which may comprise a microprocessor. The processing member 9 may also beformed by a computer, preferably a portable computer type such as apocket computer. The antennas 7 are connected to the processing member 9via a mixing device 10 or a multiplexing device by means of which thesignals from one of said pair of antennas 7 are multiplied.Consequently, the base unit 1 is arranged, by means of the processingunit 9, to analyse the signal from the transmitter unit 2 via one ofsaid pair of antennas 7 at a time in order to determine the phasedisplacement therebetween. The multiplied signal obtained is digitilisedby means of an analogue/digital converter 11. The digital signal istransmitted to a memory member 12 of the type FIFO (first in, first out)for intermediate storing. From the memory member 12, the signal issupplied to the processing member 9. By means of suitable algorithms,comprising triangulation, the direction to the transmitter unit 2 inquestion may be determined with a high accuracy. An approximate value ofthe position of the transmitter unit 2 may also be obtained. It is alsopossible to provide an analogue/digital converter 11 for each antenna 7.Thereby, the mixing device 10 may be dispensed with and the mixing maybe performed in the processing member 9 In a digital manner.

As appears from FIG. 2, the base unit 1 may also comprise a displaymember 13 in the form of a screen, for instance a LCD-screen. By meansof the display member 13, the actual position of the transmitter unit 2in question may be shown to a user. Furthermore, the base unit 1comprises a loudspeaker 14 or any similar sound generating member whichis connected to the processing member 9 and which may be arranged toproduce a warning signal to a user, for instance when the transmitterunit 2 in question and an object associated therewith is located at adistance from the base unit 1 which exceeds a predetermined level.

Each transmitter unit 2 also comprises an antenna 6 which is connectedto the transmitter member 6 for initiating the signal with a determinedfrequency. In order to differentiate the different transmitter units 2from each other, the signal from each transmitter unit 2 may comprise aunique identification protocol, ie. each transmitter unit 2 may transmita unique code which is superpositioned the determined frequency. Thecode may be generated by means of a microprocessor 16.

Furthermore, each transmitter unit 2 may comprise a receiver member 17which Is arranged to communicate with a transmitter member 18 of thebase unit 1. Thereby, the transmitter member 18 of the base unit 1 whichis connected to the processing member 9 may be arranged to transmit asignal to one of the transmitter units 2 which in turn transmits thesignal back to the base unit 1 which receives the signal via one of thereceiving antennas 7. The processing member 9 is thereby arranged tomeasure the time period from the transmission of the signal to thetransmitter unit 2 until the signal is received by the base unit 1 andby means of the time period measured to determine the absolute distancefrom the base unit 1 to the transmitter unit 2 in question. Theprocessing member 9 may comprise a pulse counter for said timemeasurement.

By means of this determination of the distance and the determination ofthe direction mentioned above, the processing member 9 may thuscalculate the position of the transmitter unit 2 in question accordingto an algorithm such as, for instance, Maximum Likelihood Estimation orGeneralised Cross Correlation.

The base unit 1 may also be arranged to transmit a signal in the form ofa transmission permission via the antenna 19 to the receiving member 17of a transmitter unit 2 in order to activate the transmitter member 6 ofthis transmitter unit 2. It is to be noted that the antenna 19 which inthe embodiment disclosed is utilised for the transmission of the signalto the transmitter unit 2 may be formed by one of the receiving antennas7. Such a receiving antenna 7 may thus have both a transmitting and areceiving function. The base unit 1 may therefore function with onlythree antennas as mentioned above. The base unit 2 disclosed hasrelatively small dimension and is advantageously designed in such amanner that it is mobile and that it may be carried by a user, i.e. thebase unit 2 is to be carried by a user when he moves within differentareas.

The communication between the receiving member 17 and the transmittermember 18 may be performed via any conventional protocol, such asCDMA-CD or Blustooth, wherein the members 6, 17 comprise amodulator/demodulator and a communication proper is performed by meansof the microprocessor. By the fact that the transmitter unit 2 thus onlyneeds to transmit the signal at determined points of time at adetermined frequency to the base unit 2 the energy consumption of thebattery 20 of the transmitter unit is reduced significantly.

The processing member 9 of the base unit i may also be arranged tolocalise a transmitter unit 2 which is moving. Thereby, the Dopplereffect may be utilised in connection with the determination of theposition and in particular for the determination of the distance.

The present invention is not limited to the embodiments disclosed butmay be varied and modified within the scope of the following claims.

What is claimed is:
 1. A device for localising a transmitter unit (2), comprising a base unit (1) and at least one such transmitter unit (2), wherein said transmitter unit (2) comprises means (4), which enable attachment of the transmitter unit (2) to an object (3), and a transmitter member (6), which is arranged to transmit a signal having a determined frequency content, wherein the base unit (1) is arranged to receive said signal and comprises at least two antennas (7), which are positioned on a relatively small distance (a) from each other and each arranged to sense such signal, and wherein the base unit (1) comprises a processing member (9), which is arranged to calculate at least the direction to said transmitter unit (2) by means of the signal sensed by the antennas (7), characterised in that said transmitter unit (2) comprises a receiver member (17), the base unit (1) comprises a transmitter member (18), and the transmitter member (18) of the base unit (1) and the receiver member (17) of the transmitter unit (2) are arranged to communicate by means of a protocol.
 2. A device according to claim 1, wherein said signal is sensed by a phase displacement between the different antennas (7), due to said distance between the antennas (7), characterised in that the processing member (9) is arranged to measure this phase displacement and to calculate said direction by means of the phase displacement measured.
 3. A device according to claim 1, characterised in that the base unit (1) is arranged to transmit a signal to said transmitter unit (2) which is arranged to transmit said signal back to the base unit (1), wherein the processing member (9) is arranged to measure the time period from the transmission of the signal to the transmitter unit (2) until the reception of the signal by the base unit (1), and by means of the time period measured determine the distance to said transmitter unit (2).
 4. A device according to claim 3, characterised in that the processing member (9) is arranged to calculate the position of said transmitter unit (2) by means of the determined distance and the determined direction.
 5. A device according to claim 4, characterised in that the base unit (1) is arranged to activate the transmitter member (6) of the transmitter unit (2) by a transmission permission which is transferred to the transmitter unit via the transmitter member (18) of the base unit and the receiver member (17) of the transmitter unit.
 6. A device according to claim 5, characterised in that the transmitter member (18) of the base unit (1) and the receiver member (17) of the transmitter unit (2) are arranged to transfer said transmission permission by means of a CDMA/CD protocol.
 7. A device according to claim 1, characterised in that each of said antennas (7) comprises an essentially straight antenna (9).
 8. A device according to claim 7, characterised in that the antennas (7) extend in essentially the same direction.
 9. A device according to claim 1, characterised in that the distance (a) between two adjacent antennas are less than one meter.
 10. A device according to claim 1, characterised in that the base unit (1) is mobile.
 11. A device according to claim 1, characterised in that the device comprises at least two transmitter units (2) and that each transmitter unit is arranged to transmit a signal according to an identification protocol and that the base unit (1) is arranged to identify the transmitter unit (2) in question by means of said identification protocol.
 12. A device according to claim 1, characterised by a display member (13) which is arranged to display information about said position of said transmitter unit (2) to a user.
 13. A device according to claim 12, characterised in that the display member (13) is an integrated part of the base unit (1) or formed by a unit, such as a computer, connected to the base unit (1). 